Broadcast radio receivers are becoming more and more portable. It is desirable, therefore, to run these portable devices on batteries. Some batteries, such as Lithium ion batteries require more extensive and costly BOMs (build of materials) than other batteries, such as alkaline batteries. For small portable radios, for example, AA and/or AAA sized alkaline batteries are often a relatively inexpensive battery solution option. In addition, rechargeable AA and AAA batteries can typically be used in devices designed for use with AA and/or AAA sized alkaline batteries.
One problem with the use of AA and/or AAA batteries (e.g., alkaline or rechargeable), however, is that these batteries often provide a limited voltage output. For example, typical alkaline or lithium AA/AAA batteries often provide a nominal output voltage of about 1.5 volts, and typical rechargeable AA/AAA batteries (NiCd, NiMH) often provide a nominal output voltage of about 1.2 volts. This limited voltage can sometimes be problematic if it is desired to power circuitry needed higher voltage levels.
To increase the voltage output, AA and/or AAA batteries can be run in series to increase the voltage output provided by these batteries. However, adding batteries causes an undesirable increase in size. Alternatively, direct-current-to-direct-current (DC-DC) voltage converters can be used to increase voltage levels. However, the problem with such a step-up DC-DC option for broadcast radio devices is that strong interference from DC-DC induced noise sources is typically caused on AM, FM, SW (short wave), and LW (long wave) audio broadcast channels at the radio device.
One prior effort to reduce the interference from these switching noise sources has been to shield the audio receiver circuitry from the switching circuitry noise sources or to increase the distance from the switching circuitry noise sources to the receiver circuitry. These solutions are somewhat effective; however, these solutions also can have the undesirable result of increasing the size and cost of the device. Another solution has been to apply spread spectrum to the DC-DC switching to spread out the impact of the switching across a wider frequency range. However, this spread spectrum solution adds further complexity and cost to the device. A more efficient and cost effective solution, therefore, is desirable.